Task 3.4: CO2 reservoir containment
Overall objective: To provide improved understanding of the fundamental effects of CO2 injection on geomechanical and sealing properties of a storage reservoir and the cap rock.
The storage part of BIGCCS is focused on developing CO2 storage-related issues to a level that enables long-term and safe storage. One of the stated goals in this part of BIGCCS is to improve the current knowledge on the interactions of CO2 with the storage volumes. This also includes interactions with the necessary sealing formations for the storage volumes.
Task 3.4 achievements thus far
Task 3.4 is a KPN associated with BIGCCS, and has funding running from January 2012 to December 2014.
The activity on near-well integrity has in the first part of the funding period focused on the possible development of near-well radial fractures as a result of the cooling effect of the injection CO2 well-stream. First modeling results indicate that fractures compromising the integrity of a sealing shale layer could develop if the well-stream is more than 50 °C colder than the formation. This situation could occur if cold CO2 from a transport ship is injected without pre-heating into a deep reservoir. The research results thus highlights the importance of proper temperature control and modeling of the effect the cooling can have on the formation.
The modeling work is followed by laboratory tests, where discs of shale rock are subjected to strong temperature variation while being constrained by a metal frame in a fixed position in such a way as to create a dilation stress strong enough to create fractures. Some development of laboratory techniques has been necessary for this work.
The focus of the activity on flow properties of faults has in the first part of the Task 3.4 funding period been to prepare a custom-made laboratory rig. The apparatus allows investigation of flow properties of a fault gouge material under very small fault shear rates and under varying normal loads.
The activity on flow properties of partially sealing rock has in the first part of the funding period concentrated on testing experimental methods for measurement of the capillary entrance pressure of low permeable rock. The method chosen is to expose one end of a water-saturated core plug to CO2 of gradually increasing pressure, while keeping the other end at a fixed pressure. The interfacial tension between CO2 and water acts together with the contact angle between CO2, water and mineral surfaces to block the CO2 from entering the pores of the rock sample until a given pressure difference (the capillary entrance pressure) is exceeded. The changed water chemistry resulting from the presence of CO2 may for some minerals lead to a change in the contact angle and thereby to a reduced entry pressure. This is the topic of the next phase of work in this activity.